Ensure any exiting hash server connection is terminated before we start
a new bitbake session. This avoids errors seen with memory resident bitbake
when the asyncio event loop isn't closed correctly.
(Bitbake rev: 42ff9de77f24e2a0bec48a14b64c4b538e00b4af)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>